1. Field of the Invention
This invention relates to a flow rate control device for a hydraulic pump which is applied mainly to a steering device of an automobile.
2. Description of the Related Art
A flow rate control device for a hydraulic pump has been disclosed, for instance, in Japanese Patent Application Examined Publication No. Hei 6-71889. The conventional flow rate control device disclosed therein comprises: a flow rate control valve that by-passes a pressure medium according to a pump discharge flow rate which changes with the speed of rotation of a pump, so that the discharge flow rate is made constant independently of the speed of rotation of the pump; and a change-over valve which operates according to a load pressure produced according to the operating condition of the steering device. That is, it is a flow rate control device of the load-sensitive type which, when the load of the steering device increases, causes the pump to increase the flow rate of operating fluid applied to the steering device.
However, as was described above, the conventional flow rate control device needs the flow rate control valve and the change-over valve which are two completely independent valves. Therefore, the flow rate control device is unavoidably bulky, thereby making it rather difficult to install it in the recently overcrowded engine room in which a large number of components have been installed. That is, it has problems to be solved for its installation in the engine room and for reduction of the weight thereof.